added some basic CLI testing, missing tests for language list and additional translation tests which can be added at will using existing tests as a template.

deep_translator/tests/test_cli.py

@@ -9,4 +9,8 @@ def results_test():
     runner = CliRunner()
     result = runner.invoke(cli.main, [ 'google', 'auto', 'en', '좋은'])
     assert result.exit_code == 0
-    assert result == 'good'
+    assert result == 'good'
+    
+    api_error = runner.invoke(cli.main, ['microsoft','auto','en','Zwei minimale Dellchen auf der Rückseite.'])
+    assert api_error.exit_code == 0
+    assert api_error == "This translator requires an api key provided through --api-key"